[WIP] Varnish Vcl generator command

[piotrkwiecinski]

Add new CLI command to allow generation of Varnish VCL configuration

Description

In addition to new CLI to generate VCL file same generator is now used in admin UI.

Fixed Issues (if relevant)

1. Create New CLI command: Generate Varnish VCL file #9199: Create New CLI command: Generate Varnish VCL file

Manual testing scenarios

1. bin/magento varnish:vcl:generate

Automated tests will be added tomorrow

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)

[adragus-inviqa]

Typo: port, not post. Also, I had a bit of problem understanding the phrase Backend port for configuration. Can we be more explicit? I know what it does, but I just think some people will need more info about it. Don't be terse on documentation.

[vrann]

Thanks for the comment. Do you have suggestions how to better call it?

[magento-team]

@piotrkwiecinski thank you for your contribution

[miguelbalparda]

@piotrkwiecinski I just saw this and I wanted to understand the code better. I couldn't find a switch for the admin value in the code and I wanted to know if this is not necessary or it is just not taken into account in this PR. Thanks!

[Ctucker9233]

@magento-team I see this PR isn't in 2.2 as of 2.2.7. Is there a backport or is this a 2.3 fix only?